1. Field of the Invention
The present invention relates generally to lubricant compositions and fasteners and, more particularly, to lubricant compositions, fasteners coated with the lubricant compositions, and method for making and using lubricant compositions and fasteners coated with such compositions.
2. Description of the Related Art
A relatively large market exists for a category of fasteners known alternatively as thread forming, thread rolling, or self-tapping fasteners. Such fasteners create strong, uniform load carrying internal threads upon installation in untapped nuts or similar members with one or more unthreaded bores. Use of such fasteners is especially prevalent in the automotive industry. Thread forming fasteners commonly are used in the automotive industry, for example, for securing components and equipment.
Different types of self-threading fasteners are available from a variety of sources, such as those carrying the trademarks TAPTITE® and TRILOBULAR™ in connection with a variety of three lobe thread forming fasteners such as screws and bolts. Thread forming fasteners are also described in various patents, including, for example, U.S. Pat. Nos. 3,978,760 and 3,803,889. Generally, a lobular thread forming fastener has a head and a threaded shank. The shank includes a threaded lobular region characterized by an arcuate polygonal, in most instances substantially triangular, pitch surface and cross-sections.
In operation, as the fasteners are driven into an untapped pilot hole of a workpiece, such as an unthreaded nut body or blank, the external threads of the thread forming fastener cut or form complementary female threads into the side wall of a pilot hole in the nut or blank, such as by a swaging operation. The resulting tight engagement between the fastener external threads and the female threads formed thereby in the workpiece is particularly advantageous and inherently provides superior resistance to vibrational loosening when compared to joints that use fasteners having pre-formed threads.
As the fastener is driven into the workpiece, the surface contact area (and hence the frictional force) between the fastener external threads and the pilot hole walls increases continuously. As the surface contact and frictional force increases, the amount of torque required to drive the fastener further into the workpiece increases. This is particularly true where the blank or nut is made of a hard metal or has a substantial thickness. Although the torque required for driving a threaded lobular fastener into an unthreaded workpiece can be significantly less than that encountered with a self-threading round-bodied thread rolling fastener, a relatively large amount of torque is still necessary to overcome the frictional forces.
The high frictional forces and large driving torque requirement inherent to a thread forming fastener has various disadvantages. For example, the high frictional forces may cause deformation of the female thread formed in the workpiece and, as a consequence, an interface mismatch may result between the fastener external thread and the workpiece female thread. These mismatches and surface-to-surface (e.g., metal-to-metal) galling effects between the fastener and the workpiece may result in fluctuating torque. Inconsistency in the required drive torque may lead to over-tightening or under-tightening of the fasteners within the workpieces. Imprecise tightening procedures can adversely affect manufacturing efficiency and the performance and appearance of the finished joint. The high frictional forces and galling effect can also lead to stripping of the fastener external threads and/or the workpiece female threads, potentially adversely impacting the clamping load of the fastener.
The vast majority of self-threading screws are applied in assemblies using automated power drivers. The clutch or related mechanisms of these power drivers are designed to disengage at precisely the same torque value each time. If the threads of the thread forming fastener or the threads formed thereby in an unthreaded nut or blank are deformed for the reasons set forth above, the driver may cease the application of force to the fastener prior to it being completely installed.
Previously, a number of lubricants have been used in connection with thread forming fasteners in an attempt to overcome some of these disadvantages. However, these lubricants have presented substantial drawbacks. For example, most of these lubricants have not provided a sufficient reduction in peak installation torque to meet or exceed current industry specifications. Additionally, although some of these lubricants have provided a significant reduction in peak installation torque, they have not exhibited the ability to significantly reduce such torque values with the necessary high degree of consistency.